Do Not Let Temperature Transients Hinder Your Build-up Pressure Interpretation – Proper Gauge Placement in Highly Productive Reservoirs in Well Testing Operations

Abstract

Quality of well testing in highly productive reservoirs directly depends on the pressure-gauge placement in the wellbore. This paper documents the impact of the placement of downhole gauges on pressure transient analysis (PTA) for high-productivity reservoirs. The article illustrates cases where this latetransient behavior is strongly influenced by temperature effects, which can lead to significant errors if not considered during the interpretation process.Although the correction of measured pressure to datum is possible by proper modeling of the influence of non-isothermal effects on the test string and the produced fluids caused by temperature changes, it is preferable to avoid this situation by suitable gauge placement. This greatly facilitates a more accurate interpretation of data using PTA with a reduced uncertainty in the definition of the appropriate reservoir model to use. Proper modeling during the test design of these temperature effects on the correction of pressure to datum also allows the determination of the resulting uncertainty pressure variations and the selection of the optimal test-string design, with consideration made to the expected temperature changes, fluid present in the wellbore, and range of productivity. Reconstruction of pressure is also possible despite a high level of resulting uncertainty.A workflow for reconstruction of pressure data taking into account temperature effects is proposed. We emphasize that such corrections cannot substitute the correct pressure measurement for successful well-test data interpretation. Present gauge technology allows proper test design and correct placement of pressure and temperature gauges in close vicinity of the interval of interest, to avoid or minimize potential problems related to the reconstruction of the measured pressure to datum.

Real Time Well Testing: A Game Changer – Experience and Lessons Learned Over 100 Well Tests Performed In the North Sea

“…In particular, a large pressure drop may occur in the tubing while the string moves between various sequences during the test. Liquid dropout and fluid segregation effects in the wellbore during pressure build-up could also mislead the interpretation, in particular in prolific formations tested under moderate drawdown (Sidorova et al, 2014). These effects can mask or at least distort the actual reservoir pressure response and can quite often lead to a misinterpretation of the well test data and a misunderstanding of the reservoir structure and associated parameters.…”

Analytical Models for Thermal Wellbore Effects on Pressure Transient Testing

“…The authors demonstrated that temperature data can provide valuable information regarding the existence of multiple fractures and any eventual crossflow between them. Sidorova et al (2014) investigated the impact of downhole gauge location on conventional pressure transient analysis in the case of high-productivity reservoirs.…”

“…Some test strings are designed with gauge adapters placed below expansion joints, hence their locations are fixed. Conversely, some test strings may account for packers that compensate for string movement (Sidorova et al, 2014). Therefore, both constant and variable pipe-length solutions will be assessed.…”

“…(3.47).The expression in Eq. (B.39) is a continuous formulation of the discrete expression proposed bySidorova et al (2014). Furthermore, the integrand inEq.…”